1. Field of the Invention
The present invention relates to a process for preparing crystalline zeolite ZSM-11 using a templating agent comprising at least one 3,5-dimethylpiperidinium (3,5-DMP) compound, and to zeolite ZSM-11 in pure phase form.
2. State of the Art
Zeolite ZSM-11 and methods for making it are known. For example, U.S. Pat. No. 3,709,979, issued Jan. 9, 1973 to Chu, discloses the preparation of ZSM-11 using quaternary cations of a Group 5-A element, such as ammonium and phosphonium compounds, as the organic templating agent. It does not, however, disclose the 3,5-DMP compounds of this invention as templating agents. U.S. Pat. No. 3,709,979 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,108,881, issued Aug. 22, 1978 to Rollman et al., teaches the synthesis of ZSM-11 using C7-C12 alkylenediamines as the organic templating agent.
U.S. Pat. No. 4,894,212, issued Jan. 16, 1990 to McWilliams et al., discloses a method for synthesizing ZSM-11 using octylamine as the organic templating agent.
U.S. Pat. No. 4,941,963, issued Jul. 17, 1990 to Valyocsik, discloses a method for synthesizing ZSM-11 from a reaction mixture containing a diquaternary ammonium templating agent.
It is alleged that pure ZSM-11 has been synthesized using tetrabutylphosphonium, tetrabutylammonium and 1,8-diaminooctane (C8) and 1,9-diaminononane (C9). See P. A. Jacobs and J. A. Martens, Studies in Surface Science and Catalysis, 33, p. 147-166.
Lok et al., in Zeolites, 3, 282-291 (1983), disclose numerous compounds which act as templating agents for the synthesis of various crystalline materials, including ZSM-11. This article does not, however, disclose the organic templating agent of the present invention for the synthesis of ZSM-11.
U.S. Pat. No. 5,213,786, issued May 25, 1993 to Beck et al., discloses the synthesis of ZSM-11 using a trimethyl ammonium cation having the formula CnN+ (CH3)3 where n is 9, 10, 11, or 12 as the organic templating agent. These trimethylammonium compounds are said to supply the proper pore-filling and charge density balance to produce ZSM-11 at the expense of ZSM-5.
It has now been found that ZSM-11 can be prepared using 3,5-DMP compounds as the templating agent and that the resulting ZSM-11 product is in pure phase form.
In accordance with the present invention, there is provided a process for preparing the zeolite ZSM-11 which comprises:
(a) preparing an aqueous solution containing sources of (1) an alkali metal oxide, alkaline earth metal oxide or mixtures thereof; (2) an oxide selected from the oxides of aluminum, boron, iron, gallium, indium, titanium, or mixtures thereof; (3) an oxide selected from oxides of silicon, germanium or mixtures thereof; and (4) at least one 3,5-dimethylpiperidinium compound;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of ZSM-11; and
(c) recovering the crystals of ZSM-11.
The present invention also provides this process further comprising replacing alkali and/or alkaline earth metal cations of the recovered ZSM-11, at least in part, by ion exchange with a cation or mixture of cations selected from the group consisting of hydrogen and hydrogen precursors, rare earth metals, and metals from Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VIB, and VIII of the Periodic Table of Elements.
The present invention also provides a crystalline material composition, as-synthesized and in the anhydrous state, whose general formula, in terms of mole ratios, is (from about 1 to about 50)Q: (from about 0.5 to about 25) M2O: (less than about 6.7)W2O3: 100 YO2 wherein: Q is a 3,5-dimethylpiperidinium compound; M is alkali metal cations and/or alkaline earth metal cations; W is aluminum, boron, gallium, indium, iron, titanium, or mixtures thereof; and Y is silicon, germanium, or mixtures thereof.
In accordance with the present invention, there is also provided the zeolite ZSM-11 having no intergrowth within its crystalline structure of any other crystalline structure. In particular, the zeolite ZSM-11 of this invention has no intergrowth of ZSM-5 crystalline structure.
The present invention further provides the zeolite ZSM-11 having no intergrowth within its crystalline structure of any other crystalline structure and having the X-ray diffraction pattern of Table I or Table II below.
The present invention also provides the zeolite ZSM-11 having a SiO2/Al2O3 mole ratio of less than 40.
Further provided in accordance with this invention is the zeolite ZSM-11 having a SiO2/Al2O3 mole ratio of less than 40 and having a cyclohexane micropore volume of at least about 0.08 ml/g.
Among other factors, the present invention is based on the discovery that the zeolite ZSM-11 can be made using 3,5-dimethylpiperidinium compounds as the organic templating agent. It is especially surprising that, by using these 3,5-dimethylpiperidinium compounds as the templating agent, ZSM-11 can be prepared in essentially pure phase form. Heretofore, it has been difficult to prepare ZSM-11 using conventional templating agents without also crystallizing the closely related zeolite ZSM-5. Also, the present invention permits the synthesis of ZSM-11 with relatively low SiO2/Al2O3 mole ratios, i.e., on the order of 25-40. In addition, it has surprisingly been found that the ZSM-11 prepared in accordance with this invention having a SiO2/Al2O3 mole ratio of less than 40 has a high cyclohexane micropore volume, ie., at least about 0.08 ml/g.
In its process embodiment the present invention comprises:
(a) preparing an aqueous solution comprising sources of oxides capable of forming ZSM-11 and at least one 3,5-dimethylpiperidinium compound;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of ZSM-11; and
(c) recovering the crystals of ZSM-11.
The Templating Agent
The templating agents useful in the present process are water-soluble 3,5-dimethylpiperidinium compounds which are capable of acting as a templating agent to form ZSM-11. They have a molecular structure of the general form: 
wherein R1 and R2 independently represent an alkyl group, either branched or unbranched, substituted or unsubstituted, containing from 1 to about 7 carbon atoms, with the proviso that R1 and R2 are not both methyl. In addition, R1 and R2 together may comprise a cyclic alkyl ring system, which, including the positively charged nitrogen atom, contains from 4 to 7 atoms, said ring system being unsubstituted or substituted with branched or unbranched alkyl groups having, e.g., one to three carbon atoms. X is an anion which is not detrimental to the formation of the ZSM-11, such as those described below. Preferred 3,5-DMP compounds are 3,5-dimethyl-N,N-diethylpiperidinium compounds; 3,5-dimethyl-N-methyl-N-ethylpiperidinium compounds; spiro 3,5-dimethylpiperidinium compounds such as 1-azonia-3,5,7-trimethyl-spiro[5.41]decane compounds.
The anion for the salt may be essentially any anion such as halide or hydroxide which is not detrimental to the formation of the molecular sieve. As used herein, xe2x80x9chalidexe2x80x9d refers to the halogen anions, particularly fluorine, chlorine, bromine, iodine, and combinations thereof. Thus, representative anions include hydroxide, acetate, sulfate, carboxylate, tetrafluoroborate, and halides such as fluoride, chloride, bromide, and iodide. Hydroxide and iodide are particularly preferred as anions.
The Preparation of ZSM-11
The process of the present invention comprises forming a reaction mixture containing sources of alkali and/or alkaline earth metal (M) cations; an oxide of aluminum, boron, iron, gallium, indium, titanium, or mixtures thereof (W); an oxide of silicon, germanium or mixtures thereof (Y); a 3,5-DMP templating agent (Q); and water, said reaction mixture having a composition in terms of mole ratios within the following ranges:
In preparing the zeolite ZSM-11 according to the present invention, the reactants and the 3,5-DMP templating agent are dissolved in water and the resulting reaction mixture is maintained at an elevated temperature until crystals are formed. The temperatures during the hydrothermal crystallization step are typically maintained from about 100xc2x0 C. to about 250xc2x0 C., preferably from about 140xc2x0 C. to about 200xc2x0 C. The crystallization period is typically greater than 1 day and generally about 1 to about 40 days. Preferably the crystallization period is from about 2 to about 20 days.
The hydrothermal crystallization is usually conducted under pressure and usually in an autoclave so that the reaction mixture is subject to autogenous pressure. The reaction mixture can be stirred during crystallization.
Once the crystals have formed, the solid product is separated from the reaction mixture by standard mechanical separation techniques, such as filtration. The crystals are water-washed and then dried, e.g., at 90xc2x0 C. to 150xc2x0 C. for from 8 to 24 hours, to obtain the as-synthesized zeolite crystals. The drying step can be performed at atmospheric or subatmospheric pressures.
During the hydrothermal crystallization step, the crystals can be allowed to nucleate spontaneously from the reaction mixture. The reaction mixture can also be seeded with ZSM-11 crystals both to direct, and accelerate the crystallization, as well as to minimize the formation of any undesired crystalline phases. When seed crystals are used, typically 0.1% to about 10% of the weight of silica used in the reaction mixture are added.
Due to the unpredictability of the factors which control nucleation and crystallization in the art of crystalline oxide synthesis, not every combination of reagents, reactant ratios, and reaction conditions will result in crystalline products. Selecting crystallization conditions which are effective for producing crystals may require routine modifications to the reaction mixture or to the reaction conditions, such as temperature, and/or crystallization time. Making these modifications are well within the capabilities of one skilled in the art.
The ZSM-11 product made by the process of this invention has an as-synthesized composition comprising, in terms of mole ratios in the anhydrous state, (from about 1 to about 50)Q: (from about 0.5 to about 25)M2O: (less than about 6.7)W2O3: 100 YO2 where M, Q, W and Y are as defined above.
The ZSM-11 product was identified by its X-ray diffraction (XRD) pattern. The X-ray powder diffraction patterns were determined by standard techniques. The radiation was the K-alpha/doublet of copper. A scintillation counter spectrometer with a strip-chart pen recorder was used. The peak heights I and the positions, as a function of 2xcex8 where xcex8 is the Bragg angle, were read from the relative intensities, 100xc3x97I/I0 where I0 is the intensity of the strongest line or peak, and d, the interplanar spacing in Angstroms corresponding to the recorded lines, can be calculated.
The X-ray diffraction pattern of Table I is representative of a calcined borosilicate ZSM-11 made in accordance with this invention. Minor variations in the diffraction pattern can result from variations in the silica-to-alumina or silica-to-boron mole ratio of the particular sample due to changes in lattice constants. In addition, sufficiently small crystals will affect the shape and intensity of peaks, leading to significant peak broadening.
The X-ray diffraction pattern of Table II is representative of a calcined all-silicate ZSM-11 made in accordance with this invention.
Calcination can also result in changes in the intensities of the peaks as well as minor shifts in the diffraction pattern. The zeolite produced by exchanging the metal or other cations present in the zeolite with various other cations (such as H+ or NH4+) yields essentially the same diffraction pattern, although again, there may be minor shifts in the interplanar spacing and variations in the relative intensities of the peaks. Notwithstanding these minor perturbations, the basic crystal lattice remains unchanged by these treatments.
The ZSM-11 of this invention is in pure phase form. As used herein, the phrase xe2x80x9cpure phase formxe2x80x9d refers to the fact that the ZSM-11 of this invention is composed of crystals having only the structure of ZSM-11, i.e., the crystals contain no other crystal structure as an intergrowth with the ZSM-11 structure. It is believed that, heretofore, although xe2x80x9cpurexe2x80x9d ZSM-11 has been reported as having been prepared, these materials have actually contained some amount of an intergrowth of another crystal structure, typically ZSM-5. One of the principal advantages of this invention is that it provides ZSM-11 without these intergrowths of other crystal structures.
It is believed that the peak in Tables I and II above found at about d=14xc3x85 demonstrates that the ZSM-11 of this invention is in pure phase form. This peak is not found in X-ray diffraction patterns of ZSM-11 which contains ZSM-5 intergrowth, and does appear in Tables I and II where it would be expected in a calculated X-ray diffraction pattern for pure phase ZSM-11. In addition, the intensities of the peaks in Tables I and II above are consistent with the intensities expected for a pure phase ZSM-11.
The ZSM-11 of this invention can be prepared having a SiO2/Al2O3 mole ratio lower than conventional ZSM-11 materials. Thus, the ZSM-11 of this invention can be made with a SiO2/Al2O3 mole ratio less than 40, preferably 35 or less, and more preferably about 30.
One surprising characteristic of the ZSM-11 of this invention which has a SiO2/Al2O3 mole ratio below 40 is that it has a high cyclohexane micropore volume. Cyclohexane micropore volume is measured by a method based on that described by G. R. Landolt in Anal. Chem., Vol. 43, No.3, 613-615, 1971. The zeolite is dried by heating overnight at 650xc2x0 F. in air. It is then loaded into ampoules, placed in the adsorption chamber and evacuated to less than one micron. Following this, the samples are connected to the adsorbate, in this case cyclohexane. The vapor pressure of the cyclohexane is measured with a pressure transducer. The samples are at 22xc2x0 C. and measurements are usually made at relative partial pressure (P/P0) of close to 0.15. The equilibration process usually takes 3-6 hours. Once the sample has equilibrated, it is removed from the chamber and reweighed to determine the amount of cyclohexane adsorbed.
Using the method described above, the ZSM-11 of this invention having a SiO2/Al2O3 mole ratio below 40 has micropore volumes of at least about 0.08 ml/g, preferably at least about 0.09 ml/g, and more preferably at least about 0.10 ml/g.
Typically, the ZSM-11 crystalline material, is thermally treated (calcined) prior to use as a catalyst. Usually, it is desirable to remove the alkali metal cation by ion exchange and replace it with hydrogen, ammonium, or any desired metal ion. The zeolite can be leached with chelating agents, e.g., EDTA or dilute acid solutions, to increase the silica/alumina mole ratio. The zeolite can also be steamed; steaming helps stabilize the crystalline lattice to attack from acids. The zeolite can be used in intimate combination with hydrogenating components, such as tungsten, vanadium molybdenum, rhenium, nickel cobalt, chromium, manganese, or a noble metal, such as palladium or platinum, for those applications in which a hydrogenation-dehydrogenation function is desired. Typical replacing cations can include hydrogen and hydrogen precursors, rare earth metals, and metals from Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VIB, and VIII of the Periodic Table of Elements. Of the replacing cations, hydrogen and cations of metals such as rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, Ga, In and Fe are particularly preferred.
The ZSM-11 prepared by the present process is useful in hydrocarbon conversion reactions. Hydrocarbon conversion reactions are chemical and catalytic processes in which carbon containing compounds are changed to different carbon containing compounds. Examples of hydrocarbon conversion reactions include catalytic cracking, hydrocracking, dewaxing, alkylation, and olefin and aromatics formation reactions.
The following examples demonstrate but do not limit the present invention.